To study the development and progression of precancerous cytologic and histopathologic changes of the anal epithelium among HIV-positive and negative homosexual men, to identify risk factors, perform dose escalation studies of isotretinoin and interferon-alpha, determine efficacy of prevention recurrence by 1)ablation alone, 2) ablation in combination with isotretinoin, 3) ablation in combination with isotretinoin and interferon-alpha.